Well, to be honest, I think I see a couple things going on.
The leaf tips and centers are showing what appears to be a little bit of nute burn/lockout. The filmy spots look like foliar spray water stains.
You say it's spreading....so I think powdery mildew, but it doesn't look like that, it looks filmy not dusty
If you are spraying your plants, especially under HID lighting, I suggest doing it when lights are out. Safer, as overspray on a hot HID light can be bad, and prevents spot burns from the intense lighting hitting standing water drops.
If you spray as your lights go out, just make sure to vent the room for an hour or two to keep the relative humidity down.
As well, I never spray ANYTHING on my plants after the first week of flowering. Not even straight water. That's just me though.